The present invention relates to an apparatus and method for the distillation, heating and storage of liquids, and more specifically to residential vapor compression distillation of water residential hot water storage. Particularly, vapor distillation is performed at least partially integrally with a storage tank which stores the hot, distilled liquid after distillation, so the distillation energy can be recovered by the stored liquid. The invention also includes an arrangement and process for automatically starting up the distillation unit with fresh feed water to enable quicker response to intermittent demands for distilled water.
Water supplied by municipalities to buildings and residences generally contains chemical impurities. These chemicals in the water can affect water odor and taste, and the water may even contain harmful quantities of mineral and biological materials. Due in large part to these potential problems with drinking water, people often install various devices to treat a portion of the water piped into their residence to remove some of the impurities. The treated water is then used for drinking and cooking.
Common methods of drinking water treatment include ion-exchange, reverse osmosis, filtration, absorption by absorbing mediums, and distillation. Each method has some drawbacks with respect to residential water treatment, however. For example, ion exchange (water softeners) generally replace calcium and magnesium ions with sodium. While this eliminates water hardness, the high sodium levels can leave undesirable deposits. Reverse osmosis is a relatively slow process which requires frequent back flushing and membrane replacement. Likewise, filtration and absorption are relatively slow, may require back flushing, and also require periodic replacement of components.
Distillation is used in some residences because it provides very pure water for drinking. Generally, in the distillation process, impure feed water is boiled to yield a distillate of pure water steam. The steam is then condensed to provide pure distilled liquid water. However, water distillation units generally operate at low distillation rates and the energy cost is relatively high. For this reason, residential distillation systems will often distill only a small supply of cold water for drinking and cooking. The relatively large supply of hot water needed for residential cleaning and bathing is generally not distilled, thereby minimizing the amount of distillation and reducing distillation costs.
According to this paradigm, wherein cold, drinking water is distilled and hot water is not distilled, there have been proposed apparatus which distill a relatively small supply of drinking water, while utilizing some of the heat given off during the distillation process to heat hot, undistilled water (e.g., for cleaning, bathing, etc.). For example, a combination apparatus for distillation of drinking water and storage of hot, undistilled water is disclosed in U.S. Pat. No. 5,348,623. A hot water heater is heated by the condensation of water being distilled and collected in separate tank. The amount of water distilled is small relative to the amount of hot, undistilled water which is stored in a hot water reservoir.
In the apparatus disclosed in U.S. Pat. No. 5,348,623, the undistilled, hot water which is stored in the hot water reservoir is heated by the heat released from the distilled water as it condenses from steam back into liquid. Since the heat of vaporization is very large relative to heat required raise the temperature of liquid water, only small amounts of distilled water can be economically generated before overheating the water in the storage tank. Of course, this may be acceptable in view of the fact that U.S. Pat. No. 5,348,623 appears to contemplate that its distilled water will only be distributed to locations where a small supply of distilled drinking water is needed, such as faucets adjacent to sinks and to ice machine. There remain problems of further maximizing the amount of distilled water while minimizing inconvenience and costs, especially energy costs.
It is an object of the present invention to provide an apparatus and process which obviates the above-described problems and shortcomings.
Another object of this invention is to provide an apparatus which distills liquid and supplies hot, distilled liquid on demand.
Another object of this invention is to provide a combination distillation unit and water heater which utilizes the technique of vapor compression distillation.
Another object of this invention is to provide a vapor compression distillation unit which has a start-up chamber which can be filled with feed water during inactive periods to facilitate quicker start-up.
It is a feature of the present invention that energy normally lost during distillation is transferred directly to the hot, distilled liquid storage tank and its distilled liquid contents. A potential advantage of this invention is that hot distilled water is produced and stored with only a small increase in energy costs over that required to operate a water heater which merely provides hot untreated water. Energy normally lost during distillation is directly transferred to pure, distilled, hot water stored in a tank.
According to the present invention, an apparatus for distilling and storing liquid includes a distillation unit for distilling liquid and a tank for storing the distilled liquid in a heated condition. The distillation unit receives feed liquid (e.g., water) and distills the feed liquid to yield distilled liquid and concentrate, wherein the distillation unit releases heat during distillation. The tank is constructed and located to be in thermal communication with the distillation unit, whereby the distilled liquid stored in the tank receives the heat lost by the distillation unit during distillation. The thermal communication between the distillation unit and the tank can be accomplished, for instance, by placing the distillation unit inside of the tank.
According to a further aspect of the present invention, the distillation unit distills liquid by vapor compression distillation. This vapor compression distillation requires less net energy than other distillation methods because most of the heat of condensation is recovered. Also, the heat given off by a vapor compression distillation unit will often be roughly commensurate with the heat which can be usefully applied to maintain water in a residential water heater at an appropriate elevated temperature and to heat untreated feed water as it is coming into the distillation unit.
According to some embodiments of the present invention, the vapor compression unit contains a start-up chamber and a boiler chamber. Storing untreated feed water in the start-up chamber during periods of inactivity can facilitate quicker start-up of the distillation unit. Specifically, with a start-up chamber, the untreated feed water needed to start up distillation is maintained in close physical proximity to and in thermal communication with the boiler chamber, and it will be somewhat preheated by heat transferred from the hot distilled water storage tank. The start-up chamber can be utilized to obtain a low distillation pressure in the boiler of the distillation unit. Also, the use of a start-up chamber allows distillation to commence on fresh, new feed water, rather than old concentrate.